1. Field of the Invention
The present invention relates to pixel structures for use in electroluminescent panels, and more particularly, to a pixel structure having high precision and a related fabrication method.
2. Description of the Prior Art
An electroluminescent display, such as an organic light emitting diode (OLED) display, is growing in popularity as a mainstream type of thin, flat display, due to characteristics of small size, high resolution, high contrast ratio, low power consumption and active luminescence.
A color image frame of the electroluminescent display is primarily provided by a plurality of display pixels comprising red, green and blue subpixels, and the color image frame is composed of different combinations of grey level color values displayed by the red, green and blue subpixels of each display pixel while the image frame is being displayed.
A pixel structure of the electroluminescent display is an arrangement of the red, green and blue subpixels, and a resolution of the electroluminescent display is heavily influenced by a design of the pixel structure. Recently, the most popular pixel structure for use in the electroluminescent display is a stripe. Please refer to FIG. 1, which is a schematic diagram of a prior art stripe pixel structure. As shown in FIG. 1, the stripe pixel structure 10 comprises a plurality of red subpixels R, a plurality of green subpixels G, and a plurality of blue subpixels B, wherein the red subpixels R, the green subpixels G, and the blue subpixels B are arranged in respective stripe formations. In other words, each column of the stripe pixel structure 10 comprises subpixels of one color, and the columns are arranged in an order of red, green, then blue. The stripe pixel structure 10 comprises a plurality of display pixel units 12, and each display pixel unit 12 comprises a red subpixel R, a green subpixel G, and a blue subpixel B adjacent to each other and in a same row.
Although the pattern arrangement of the stripe pixel structure 10 is simple, a limitation exists when making a shadow mask used in an evaporation deposition process. Please refer to FIG. 2, which is a schematic diagram of the shadow mask utilized to make the stripe pixel structure of FIG. 1. As shown in FIG. 2, the shadow mask 14 comprises a plurality of rectangular openings 16, and each rectangular opening 16 corresponds to the plurality of subpixels of a single color, such as the plurality of red subpixels. However, because the shadow mask 14 is made of a metallic material, a gap between adjacent rectangular openings 16 must be sufficiently large (as indicated by an arrow of FIG. 1) to allow the shadow mask 14 to maintain structural strength, which establishes a lower limit on a density of the subpixels, affecting a maximum resolution achievable in the electroluminescent display.
Please refer to FIG. 3, which is a schematic diagram of another prior art pixel structure 20. The pixel structure 20 comprises a plurality of red subpixel units 22R, a plurality of green subpixel units 22G and a plurality of blue subpixel units 22B, wherein each subpixel unit has four subpixels of a same color arranged in a matrix, and the red subpixel unit 22R, the green subpixel unit 22G and the blue subpixel unit 22B are arranged in an alternating formation, as shown in FIG. 3. A display pixel unit 24 of pixel structure 20 consists of four subpixels (represented by a dotted line) from four adjacent subpixel units, respectively. In other words, the display pixel unit 24 at least comprises a red subpixel R, a green subpixel G, and a blue subpixel B, and further comprises another subpixel that may be a red subpixel R, a green subpixel G, or a blue subpixel B.
Although the arrangement of FIG. 3 exhibits better color performance than the stripe pixel structure of FIG. 1, the resolution cannot be further increased because of process limitations. The pixel structure of the electroluminescent panel generally utilizes an evaporation deposition process with a shadow mask having different opening patterns to fabricate the red subpixel unit, the green subpixel unit, and the blue subpixel unit, respectively. However, the arrangement of the red subpixel unit 22R, the green subpixel unit 22G and the blue subpixel unit 22B in the pixel structure 20 will similarly encounter the process limitation of the evaporation deposition process.
Please refer to FIG. 4, which is a schematic diagram of the shadow mask used to fabricate the pixel structure 20 of FIG. 3. As shown in FIG. 4, the shadow mask 30 comprises a plurality of rectangular openings 32, and each rectangular opening 32 corresponds to the subpixel units of a single color, such as the red subpixel units. The subpixel unit can be deposited onto a substrate of the electroluminescent panel through use of the shadow mask 30 by evaporation. As mentioned above, because the shadow mask 30 is made of a metallic material, a distance between adjacent rectangular openings 32 must be sufficiently large (as shown by an arrow in FIG. 4) to maintain a structural strength of the shadow mask 30. Thus, a lower limit on a density of the subpixels will be unable to decrease, which affects a resolution of the display.